The present invention relates to the field of data transmission systems, particularly data transmission systems suitable for use in downhole environments, such as along a drill string used in oil and gas exploration, or along the casings and other equipment used in oil and gas production.
The goal of accessing data from a drill string has been expressed for more than half a century. As exploration and drilling technology has improved, this goal has become more important in the industry for successful oil, gas, and geothermal well exploration and production. For example, to take advantage of the several advances in the design of various tools and techniques for oil and gas exploration, it would be beneficial to have real time data such as temperature, pressure, inclination, salinity, etc. Several attempts have been made to devise a successful system for accessing such drill string data. These systems can be broken down into four general categories.
The first category includes systems that record data downhole in a module that is periodically retrieved, typically when the drill string is lifted from the hole to change drill bits or the like. Examples of such systems are disclosed in the following U.S. Pat. Nos.: 3,713,334; 4,661,932 and 4,660,638. Naturally, these systems have the disadvantage that the data is not available to the drill operator in real time.
A second category includes systems that use pressure impulses transmitted through the drilling fluid as a means for data communication. For example, see U.S. Pat. No. 3,713,089. The chief drawbacks to this mud pulse system are that the data rate is slow, i.e. less than 10 baud; the system is complex and expensive; the results can be inconsistent; and the range of performance can be limited. In spite of these drawbacks, it is believed that this mud pulse system is the only real time data transmission system currently in commercial use.
The third category includes systems that transmit data along an electrical conductor that is integrated by some means into the drill string. Examples of such systems are disclosed in the following U.S. Pat. Nos.: 3,879,097; 4,445,734 and 4,953,636. Because the drill string can be comprised of several hundred sections of drill pipe, it is desirable to locate the electrical system within each section of pipe and then provide for electrical connections when the sections are joined together. A decided drawback of such systems is the fact that the downhole environment is quite harsh. The drilling mud pumped through the drill string is abrasive and typically has a high salt content. In addition, the downhole environment typically involves high pressures and temperatures. Moreover, heavy grease is typically applied at the joints between pipe sections. Consequently, the reliance on an electrical contact between joined pipe sections is typically fraught with problems.
A fourth category includes systems that use a combination of electrical and magnetic principles. In particular, such systems have an electrical conductor running the length of the drill pipe and then convert the electrical signal into a corresponding magnetic field at one end. This magnetic field is passed to the adjacent drill pipe and then converted to back to an electrical signal. Examples of such systems are described below.
U.S. Pat. No. 2,379,800 to Hare describes a system with a primary transformer coil, consisting of a wire wound around a soft iron core, being installed within an annular groove at one end of the pipe and a similar, secondary transformer coil, being installed within an annular groove at the other end of the pipe. When the pipes are connected, the primary and secondary coils are brought close together. Once the signal is transmitted across the joint, it is carried along the drill pipe by a wire connected to the coil in the opposite end of the pipe. This system also included condensers, rectifiers, and amplifiers to aid the transmission of the signal from one pipe to another.
U.S. Pat. No. 2,414,719 to Cloud, discloses a serial inductive coupling system including a series capacitor in each link to tune the system to a given pass band, typically around 3 kHz. The capacitor has the undesired feature of providing a narrow bandwidth. Cloud also suggested the use of a U-shaped trough of a xe2x80x9cmagnetic memberxe2x80x9d (see reference numeral 56 in FIG. 9). The materials suggested for this magnetic member include xe2x80x9cArmco iron, nickel alloy, and magnetic steel.xe2x80x9d All of these materials conduct electricity. As such, it is believed that eddy currents develop in this magnetic member, thereby lowering the efficiency of the system.
U.S. Pat. No. 3,090,031 to Lord proposed an improvement to the Hare Patent to help reduce the power required in the transformer system. Lord""s patent describes a circuit similar to Hare""s but with the addition of a transistor and the use of mercury-type penlight batteries as a power source at each joint. As an alternative power source, he proposed the use of chemical additives to the drilling fluid that could provide power to the transformers by electrolytic action.
U.S. Pat. No. 4,788,544 to Howard describes a system that utilized a Hall Effect sensor as a means to bridge the drill pipe joint. In this system, an electromagnetic field generating coil having a ferrite core is employed to transmit data signals across the joint. The magnetic field is sensed in the adjacent pipe through a xe2x80x9cHall effect sensorxe2x80x9d (no relation to the present inventors). The Hall effect sensor produces an electrical signal corresponding to the magnetic field strength and sends the signal along a conductor wire to the coil at the next joint.
Although U.S. Pat. Nos. 4,806,928 and 4,901,069 to Veneruso do not describe a system that is incorporated into individual sections of drill pipe; these patents do show a system for electromagnetic coupling a cable passing through the well bore to a downhole tool. The system described includes inner and outer induction coils which are cooperatively arranged and adapted so that one of coils can be dependently suspended from a well bore cable and lowered into coaxial alignment with the other coil that is positioned within the well bore and electrically connected to a down hole apparatus.
Another example of a downhole data transmission system that uses the principles of induction is described in U.S. Pat. No. 4,605,268 to Meador. This patent shows a current-coupled system that uses two toroidal coils at each joint. Each coil is confined within an electrically conducting housing. A first electrically conducting housing surrounding the first coil, located in the end of one drill string component, is electrically connected to a second electrically conducting housing for the second coil, located in the end of the adjacent drill string component. In this way, as an electrical current is induced by the first coil in the first electrically conducting housing, that electrical current is conducted to the second electrically conducting housing, whereupon, a magnetic field is induced in the second coil. Thus, although the principles of induction are used, the system in the 268 patent relies on an electrical connection between adjacent components of the drill string. As such, it is subject to the problems described above in connection with the third category of systems.
Briefly stated, the invention is a system for transmitting data through a string of downhole components.
In accordance with one aspect of the invention, the system includes a plurality of downhole components, such as section of pipe in a drill string. Each component has a first end and a second end, the first end of one downhole component being adapted to be connected to the second end of another downhole component.
Located proximate to the first end is a first magnetically conductive, electrically insulating element. This element includes a first U-shaped trough with a bottom, first and second sides and an opening between the two sides. A second magnetically conductive, electrically insulating element is located proximate the second end of each downhole component. This second element likewise includes a second U-shaped trough with a bottom, first and second sides and an opening between the two sides. The first and second troughs are configured so that the respective first and second sides and openings of the first and second troughs of connected components are substantially proximate to and substantially aligned with each other.
A first electrically conducting coil is located in each first trough, while a second electrically conducting coil is located in each second trough.
An electrical conductor is in electrical communication with and runs between each first and second coil in each component.
In operation, a varying current applied to a first coil in one component generates a varying magnetic field in the first magnetically conductive, electrically insulating element, which varying magnetic field is conducted to and thereby produces a varying magnetic field in the second magnetically conductive, electrically insulating element of a connected component, which magnetic field thereby generates a varying electrical current in the second coil in the connected component.
In accordance with another aspect of the invention, the system includes a plurality of downhole components, each with a pin end and a box end. Each pin end includes external threads tapering to a pin face, while each box end includes internal threads tapering to a shoulder face within the box end. The pin face and shoulder face are aligned with and proximate each other when the pin end of the one component is threaded into a box end of the other component. A first inductive coil located within a recess formed in each pin face, while a second inductive coil located within a recess formed in each shoulder face. An electrical conductor is included which is in electrical communication with and runs between each first and second coil in each component.
In accordance with another aspect of the invention, the system includes a plurality of downhole components, each with a first end and a second end, the first end of one downhole component being adapted to be connected to the second end of another downhole component. A first electrically conducting coil having no more than five turns, and preferably no more than two, most preferably no more than one, is placed at each first end, while a second electrically conducting coil having no more than five turns, and preferably no more than two, most preferably no more than one, is placed at each second end. The first and second coils of connected components are configured so as to be substantially proximate to and substantially aligned with each other. An electrical conductor is provided which is in electrical communication with and runs between each first and second coil in each component. In operation, a varying current applied to a first coil in one component generates a varying magnetic field, which magnetic field induces a varying electrical current in the second coil in the connected component, to thereby transmit a data signal.
In accordance with another aspect, the invention is a downhole tool adapted to transmit data over the systems described above.
The present invention provides the advantage that, as the data transmission line uses alternating conductive and inductive elements, the inductive elements at the end of each segment enable the transmission line to be lengthened or shortened during drilling operations without need for an electrically conductive path across the joint. Indeed, the only closed electrical path is within each individual element, which constitutes a single closed path for electrical current.
It should be noted that, as used herein, the term xe2x80x9cdownholexe2x80x9d is intended to have a relatively broad meaning, including such environments as drilling in oil and gas, gas and geothermal exploration, the systems of casings and other equipment used in oil, gas and geothermal production.
It should also be noted that the term xe2x80x9ctransmissionxe2x80x9d as used in connection with the phrase data transmission or the like, is intended to have a relatively broad meaning, referring to the passage of signals in at least one direction from one point to another.
It should further be noted that the term xe2x80x9cmagnetically conductivexe2x80x9d refers to a material having a magnetic permeability greater than that of air.
It should further be noted that the term xe2x80x9celectrically insulatingxe2x80x9d means having a high electrical resistivity, preferably greater than that of steel.